A core, which is a sand mold that is inserted into a casting mold as a part corresponding to a cavity when, in particular, a casting having a complicated cavity therein is produced, is produced by packing sand into a mold. A complicated shape is formed by placing a core in a casting mold called main mold, casting a molten metal, such as iron, and solidifying it into a shape, and finally breaking the core. For example, because the melting temperature of iron is approximately 1500° C., sand with a special composition is used so that the core can withstand such high heat. After the product is half cooled, the core is broken by applying an impact and the sand is taken out. Thus, each core is expendable without exception. The sand used to form a core is limited to those of a predetermined type, size or the like, and the properties a core is required to have include: (a) having high heat resistance, (b) generating only a small amount of gas and having a gas drainage, (c) being excellent in sand collapsibility, and (d) being low in cost. Currently, the core sand is mainly imported from Australia.
A core is produced by putting a mixture of predetermined sand with a binding substance (which is hereinafter referred to as “binder”) into a mold and shaping the sand by, for example, applying heat. Cores are expendable, and used cores are crushed and reduced to sand. However, because the sand used to form cores has to be of a predetermined type and particle size and has a relatively high unit price, the sand once used as a core needs to be recycled, in other words, regenerated. However, used core sand has a binder adhering to the surface thereof, and the adhering binder has to be removed in order to regenerate the used core sand. Methods for removal of the binder include a method using a mechanical or physical action and a method using combustion or the like as described later. There are organic and inorganic binders. Currently, organic binders are widely used, but the use of inorganic binders is increasing because of the effect of volatile organic compounds (VOC). Inorganic binders have a higher melting point and are therefore more difficult to remove than organic binders by a method of removing a binder by combustion. In a conventional core sand regeneration system, an inorganic binder sometimes causes formation of silicon threads between the sand particles that bring the sand into a condition that cannot be regarded as having been regenerated.
Many manufacturers of transportation machines are located and their peripheral technologies have been developed in the region where the inventor of this application lives. Under such environment, the inventor of this application has been engaging in the business of producing and selling what they call kneading mixers for stirring and mixing core sand and a binder, their related equipment and so on. In order to address the above problem, the inventor of this application manufactured a prototype of a system that can regenerate used core sand with inorganic binder as well as used core sand with an organic binder. The inventor of this application focused on the fact that inorganic binders have a higher melting point than organic binders, and took care so that the combustion temperature could be high, the surface of the crushed used core sand could be combusted uniformly and the used core sand cannot be exposed to the direct flame of the burner. Then, as a result of trial and error, the inventor of this application invented a rotary kiln-type core sand regeneration system and filed an application for a patent on 27 Nov. 2015 (Heisei 27) (JP Patent Application 2015-231682, which is hereinafter referred to as “prior application”).
When produced and sold, and started to be used in core producing companies and so on, the rotary kiln-type core sand regeneration system according to the invention of the prior application attracted attention among the people in the industry who heard about the effect of it and came to see it. The inventor of this application heard voices from the people in the industry saying “We want a more compact core sand regeneration system because of the limited premises.” or “We want a core sand regeneration system that can regenerate core sand in a shorter period of time and save energy.” Thus, the inventor of this application invented an energy-saving, batch-type core sand regeneration system that can regenerate used core sand in a shorter period of time by downsizing the core sand regeneration system of the prior application and filed an application for a patent on 27 Jan. 2016 (Heisei 28) (JP Patent Application 2016-013869, which is hereinafter referred to as “later application). This application collects the inventions according to the prior application as first to sixth inventions and the inventions according to the later application as seventh to thirteenth inventions.
The following documents are found as related art documents relating to a core sand regenerate method:                a regeneration method for regenerating used casting sand by breaking the casting mold after casting followed by crushing the used casting sand into individual sand particles, applying a mechanical impact to the sand particles sufficient to break the binding substance covering the outer surface thereof, washing the sand particles with water to remove substantially all the binding substance still adhering to the sand particles therefrom due to charge with static electricity (Patent Document 1);        a casting sand regeneration method including a roasting step of roasting black sand to convert the uncombusted inorganic substance, such as bentonite, adhering to the surface of the black sand into a magnetic material, a scraping step of scraping the magnetic material layer off the surface of the black sand treated in the roasting step with grinding stones, and a magnetic separation step of separating the magnetic material scraped off in the scraping step from the black sand using magnetic force to obtain regenerated sand (Patent Document 2);        a solution furnace for solution treatment of an aluminum cast casted using a mold provided with a sand core, including a first heat treatment furnace having an inlet through which a cast after casting and before sand removal is introduced, a second heat treatment furnace having a discharge port, a shutter provided between the first heat treatment furnace and the second heat treatment furnace, a cast transporting conveyer for transporting the cast from the inlet to the discharge port, and a sand transporting conveyer provided below the cast transporting conveyer in the first heat treatment furnace, the cast transporting conveyer having a cast carrying surface with a mesh-like structure so that the core sand resulting from collapse of the sand core can pass downward through it and fall onto the sand transporting conveyer (Patent Document 3); and        a method for regenerating casting sand used in a production process characterized by including the steps of preparing a rotor and a drum located in the rotor and having a striking means, loading the drum with a batch amount of sand, exposing the sand to high-density striking, shear and friction forces, and adjusting the variable rotational speed of at least one of the drum and rotor to adapt the strength of the forces to the force necessary to wash quartz particles (Patent Document 4).        